With the continuous development of science and technology, a laser technique has been widely applied to such fields as laser manufacturing, micro machining, laser guidance, optical storage, laser medicine, etc. During the practical application process of laser, light beam quality means to evaluate the laser on the aspect of quality, which has significant meaning on designing, manufacturing, detecting and applying the laser, etc. There have been multiple index parameters for evaluating the laser beam quality at present. Different light beam quality definitions correspond to different application objects, which also reflect different emphasis points of the light beam quality. Therefore, the light beam quality shall be evaluated according to the specific application object.
In addition, the laser spot size, beam waist size, energy distribution, phase distribution, and angle of divergence are also important parameters for measuring the performances of an optical maser. During the practical application of laser, the requirements on the spot quality formed by an optical system are higher and higher. The measurement and analysis of the laser spot are very important to evaluate the imaging quality of the optical system and the stability of the laser beam, and the like; therefore, it is necessary to conduct accurate measurement and analysis on laser beam spots.
Common methods for measuring the laser beam spot sizes include an over-coring method, a knife-edge method and a CCD method. The over-coring method means to shade light using a radius-variable round diaphragm, and calculates the laser spot size through calculating percentage ratios of energies shaded and a diaphragm radius. This method needs to align the center of the diaphragm with the center of the spot, which is relatively difficult in actual operation. The knife-edge method employs a measurement method based on total transmittance, wherein a transmittance function thereof is a step function, and allows the distance between two power thresholds during the moving process of the blade to be defined as the spot size by setting a certain power threshold and pushing a blade along a certain direction. This method is simple in principle, but needs a high precision moving device. The method for measuring laser beam spot size based on a CCD camera has such features as high spatial resolution, wide application range, and flexible computational algorithm, and has become a common method for measuring laser beam spot size. The method for measuring laser beam spot size based on a CCD camera includes a 1/e2 definition method and a secondary moment definition method based on moment inalterability provided by the International Standard Organization, however both the two methods need to conduct strict decay on incident light intensity, moreover in order to ensure the precision, overexposure of a collection camera shall be prevented, and spot image grey values shall be controlled in a certain scope, resulting in complicated operation and poor robustness.